This study of hormonal regulation is targeted to define the biochemical mechanisms whereby age-dependent changes perturb physiological control systems and, thus, lead to a failure to maintain homeostasis in the aged. Investigations are focused on the biochemical interactions of hormones, which are mediated via cyclic AMP and cyclic GMP. Topics investigated include: 1) hormone receptors in membranes; 2) adenylate cyclase and guanylate cyclase activities; 3) phosphorylation of membrane proteins by cyclic nucleotide-dependent and -independent protein kinases; 4) control of cyclic nucleotide levels by regulation of phosphodiesterase activities. Hormonal regulatory systems in kidney, heart, brain, colon, aorta, and ductus deferens were studied. BIBLIOGRAPHIC REFERENCES: Filburn, C.R. and Wyatt, G.R.: Adenylate and guanylate cyclases of cecropia silkmoth fat body. J. Insect Physiol. 22: 1635-1640, 1976. George, E.R., Balakir, R.A., Filburn, C.F. and Sacktor, B.: Cyclic adenosine monophosphate-dependent and -independent protein kinase activity of renal brush border membranes. Arch. Biochem. Biophys. 180: 429-443, 1977.